The dentate gyrus (DG) is a region of cerebral cortex in the medial temporal lobe that is frequently involved in epilepsy and other neurodevelopmental disorders. Interestingly, DG neurogenesis is extremely prolonged relative to other cortical areas, and depends on migrations of progenitor cells within the dentate migration stream (DMS) and other transient neurogenic niches. Previous studies from the PI's lab have shown that one type of cortical progenitor cells, known as intermediate progenitors (IPs) or transit-amplifying cells, specifically express Tbr2, a T-box transcription factor, during DG development as well as adult neurogenesis. New preliminary data show that Tbr2+ IPs plays major roles in transient neurogenic niches and dentate migration streams that are essential to morphogenesis of the dentate gyrus. For example, Tbr2+ IPs appear to pioneer the DMS and enhance the subsequent migration of neural stem cell (NSC)-like radial glial progenitors (RGPs). Aims 1 and 2 of this project will analyze transient DG niches and cell migrations in mice, and determine the roles of RGPs and IPs in gyrogenesis (development of convoluted cortex). Aim 3 extends these approaches to characterize DG malformations in mutant mice with defects of IP or radial glial progenitor (RGP) differentiation.